1. Field of the Invention
The present invention relates to a liquid crystal display and, more particularly, to a thin film transistor liquid crystal display capable of preventing bright line generation due to adsorption of residual ions in pixels adjacent to a gate pad unit.
2. Description of the Prior Arts
As is generally known, a liquid crystal display has a structure that a plurality of gate bus lines and data bus lines are cross-arranged to define unit pixels and thin film transistors are arranged at the intersection thereof.
A pixel electrode is arranged on each pixel to be in contact with a drain electrode of the thin film transistor. The plurality of data bus lines are in contact with a source electrode of the thin film transistor for applying graphic signals.
A common bus line, which regularly applies predetermined common signals, is arranged to form storage capacitor, being in contact with a predetermined part of the pixel electrode.
According to the liquid crystal display, when driving signals are applied to a plurality of gate pad units, they are transmitted along a gate bus line. Then, when the thin film transistor is turned on, graphic signals, applied along the data bus line, are applied to the pixel electrode through a channel layer of the thin film transistor, thereby realizing a desired graphic.
As described above, a storage common structure is divided into a pi (π) structure and a linear structure. In the pi structure, a common bus line applying common signals has branches overlapped with a predetermined part of pixel electrode and both sides thereof. And, in the linear structure, the common bus line is arranged on lower part of the pixel electrode to be parallel with the gate bus line.
FIG. 1 is a drawing showing a thin film transistor liquid crystal display having a common bus line of a pi (π) structure according to a conventional art. As shown in the drawing, a plurality of gate bus lines 1 and a plurality of data bus lines 5 are cross-arranged to define a unit pixel, and thin film transistors 7 are arranged at the intersection thereof, as a switching device.
A common bus line 3, in contact with a common pad unit 20, has a branch overlapped with a predetermined part of a pixel electrode (not illustrated) on the upper part and both sides thereof. The common bus line 3 applies predetermined common signals with a regular cycle.
In the drawing, a reference code 10 is a gate pad unit and a reference code 6 is residual ion.
FIG. 2 is a drawing showing a thin film transistor liquid crystal display having a common bus line of linear type according to a conventional art. As shown in the drawing, it has the same structure to FIG. 1 except that the common bus line 13 is arranged on the center of pixel region, parallel with the gate bus line 11.
In the liquid crystal display having the structure, driving signals are applied to the gate pad unit 10 and then, sequentially applied to each pixel through the gate bus line 11 in contact with the gate pad unit 10, wherein common signals are regularly inputted in the common pad unit 40 and then, applied to each pixel through the common bus line 13. A reference code 19 is a pixel electrode.
However, the above-identified liquid crystal display has a disadvantage that the pixels adjacent to the gate pad unit have data bus lines not symmetrically on both sides thereof, thereby generating adsorption of residual ions 6 due to the asymmetrical structure and voltage difference of gate signal and common signal in signal application. The adsorbed residual ions form an electric field and cause light leakage on the outmost pixels in display. As a result, the screen quality is deteriorated.
Referring to FIG. 1, in the pi (π) shape common bus line, branches are formed along a pixel opening to be overlapped with the upper part of pixel electrode and in contact with both sides thereof, thereby shielding diffusion of residual ions to some extent. However, on the lower part, adsorption of residual ions 6 is generated since it is difficult to shield diffusion by the gap between branch and gate bus line 1.
Referring to FIG. 2, when the common bus line is formed in a linear shape, adsorption of residual ions 16 is generated on both upper and lower parts of pixel regions since there is no common bus line 13 operating as a shield thereon.